Many diseases and conditions of acute or chronic injury have an inflammatory and/or cell death component to them. These disorders can result from a disruption in the homeostatic balance between beneficial and detrimental responses of the organism. For example, there may be a decrease in the production of trophic molecules that mediate cell survival and other beneficial cellular processes, or there may be an overproduction of pro-inflammatory or other detrimental molecules that mediate toxic cellular responses. It is also becoming increasingly appreciated that dysregulation of signal transduction pathways involving protein kinases may be involved in the generation or progression of these diseases. Thus, development of new classes of cell permeable ligands or protein kinase inhibitors that can modulate disease-relevant pathways is an important area for therapeutics. The current invention relates generally to the development of a new class of pyridazine and/or related heterocyclic derivatives that have utility for selective modulation of cellular pathways linked to disease progression and/or protein kinase inhibition relevant to inflammation and/or cell death. In addition to a variety of heterocyclic compositions having utilities including those mentioned above, the present invention also includes various methods relating to the modulation of signal transduction pathways and/or new therapeutic routes relating thereto.
Neuroinflammation is a characteristic feature of disease pathology and progression in a diverse array of neurodegenerative disorders that are increasing in their societal impact (for a recent review, see, e.g., Prusiner, S. B. (2001) New Engl. J. Med. 344, 1516-1526). These neuroinflammation-related disorders include Alzheimer's disease (AD), amyotrophic lateral sclerosis, autoimmune disorders, prion diseases, stroke and traumatic brain injury. Neuroinflammation is brought about by glial (astrocytes and microglia) activation, which normally serves a beneficial role as part of an organism's homeostatic response to injury or developmental change. However, dysregulation of this process through chronic or excessive activation of glia can contribute to the disease process through the increased production of proinflammatory cytokines and chemokines, oxidative stress-related enzymes, acute phase proteins, and various components of the complement cascades. (See, e.g., Akiyama, H., Barger, S., Bamum, S., Bradt, B., Bauer, J., Cole, G. M., Cooper, N. R., Eikelenboom, P., Emmerling, M., Fiebich, B. L., Finch, C. F., Frautschy, S., Griffin, W. S., Hampel, H., Hull, M., Landreth, G., Lue, L., Mrak, R., Mackenzie, I. R., McGeer, P. L., O'Banion, M. K., Pachter, J., Pasinetti, G., Plata-Salaman, C., Rogers, J., Rydel, R., Shen, Y., Streit, W., Strohmeyer, R., Tooyoma, I., Van Muiswinkel, F. L., Veerhuis, R., Walker, D., Webster, S., Wegrzyniak, B., Wenk, G., and Wyss-Coray, T. (2000) Neurobiol. Aging 21, 383-421). The direct linkage of glial activation to the pathology, that is a hallmark of disease, underscores the importance of understanding the signal transduction pathways that mediate these critical glial cellular responses and the discovery of cell permeable ligands that can modulate these disease relevant pathways.
In the case of AD, the deposition of β-amyloid (Aβ) and neurofibrillary tangles is associated with glial activation, neuronal loss and cognitive decline. Id. In terms of molecular mechanisms, there is increased expression of nitric oxide synthase (NOS) in glial cells surrounding the characteristic amyloid plaques; there is neuropathological evidence of peroxynitrite-mediated neuronal damage; and there is evidence that nitric oxide (NO) overproduction is involved in mechanisms of Aβ-induced brain dysfunction. NOSII (iNOS) is induced as part of the glial activation response and is an oxidative stress-related enzyme which generates NO. When NO is present in high levels along with superoxide, the highly reactive NO-derived molecule peroxynitrite is generated, which can lead to neuronal cell death. The proinflammatory cytokine IL-1β is also overexpressed in activated glia in AD brain and polymorphisms in IL-1β genes are associated with an increased risk of early onset sporadic AD (See, e.g., Du, Y., Dodel, R. C., Eastwood, B. J., Bales, K. R., Gao, F., Lohmuller, F., Muller, U., Kurz, A., Zimmer, R., Evans, R. M., Hake, A., Gasser, T., Oertel, W. H., Griffin, W. S. T., Paul, S. M., and Farlow, M. R. (2000) Neurology 55, 480-483), IL-1β can also influence amyloid plaque development and is involved in additional glial inflammatory and neuronal dysfunction responses (See, e.g., Griffin, W. S. T., Sheng, J. G., Royston, M. C., Gentleman, S. M., McKenzie, J. E., Graham, D. I., Roberts, G. W., and Mrak, R. E. (1998) Brain Pathol. 8, 65-72; and Sheng, J. G., Ito, K., Skinner, R. D., Mrak, R. E., Rovnaghi, C. R., Van Eldik, L. J., and Griffin, W. S. T. (1996) Neurobiol. Aging 17, 761-766). These selected examples are part of a large body of evidence accumulated over the past decade that directly links glial activation and specific glial products to neurodegenerative disorders, and raise the possibility that selective modulation of glial activation pathways linked to disease progression might be an area for discovery of new therapies.
A related concern appears to be protein kinase deregulation. Protein kinases are a large family of proteins that play an import role in signalling pathways regulating a number of cellular functions, such as cell growth, differentiation and death. The human genome project has revealed that 20% of the—32,000 human genes encode proteins involved in signal transduction. Among these are more than 500 protein kinases and 130 protein phosphatases exerting tight control on protein phosphorylation. Each protein kinase transfers the γ-phosphate of ATP to a specific residue(s) of a protein substrate. Protein kinases can be further categorized as tyrosine, serine/threonine or dual specific based on acceptor residue. Examples of serine/threonine kinases include MAP kinase, MAPK kinase (MEK), Akt/PKB, Jun kinase (JNK), CDKs, protein kinase A (PKA), protein kinase C (PKC), and calmodulin (CaM)-dependent kinases (CaMKs). A large number of viral oncogenes were found to encode activated protein kinases, implicating deregulated kinases in human cancers. Abnormal protein phosphorylation also underlies many other diseases including diabetes, rheumatoid arthritis and hypertension. Since the hyperactivity of kinases is implicated in disease states, kinase inhibitors could be important therapeutic agents. These inhibitors could be designed to compete either against ATP or the protein substrate.
The potential for modulation of glial inflammatory processes as a therapeutic approach to neurodegenerative disease is indicated by both epidemiological and clinical trial data that show that the use of anti-inflammatory compounds delays onset or slows progression of neurodegenerative changes. Currently, there is a need to develop new classes of chemical compounds capable of inhibiting proinflammatory and oxidative stress related pathways in activated glia as a prelude to searches for new therapeutic approaches. Relevant to this unmet need, through the use of cell-based, high throughput screens (HTS) experimental anti-inflammatory drugs in the family of indolocarbazole alkaloids were found to have a variety of protein kinase inhibitory activities and inhibit NOS and IL-1β production in activated glia. Although the indolocarbazole alkaloid drugs failed as therapeutics due to toxicology, closely related indolocarbazole compounds with more selective kinase inhibitory activity are less toxic and show promise as experimental therapeutics (See, e.g., Maroney, A. C., Finn, J. P., Bozyczko-Coyne, D., O'Kane, T. M., Neff, N. T., Tolkovsky, A. M., Park, D. S., Yun, C., Yan, I., Troy, C. M., and Greene, L. A. (1999) J. Neurochem. 73, 1901-1912; and Pirvola, U., Xing-Qun, L., Virkkala, J., Saarma, M., Murakata, C., Camoratto, A. M., Walton, K. M., and Ylikoski, J. (2000) J. Neurosci. 20, 43-50). While the effects of these compounds include inhibition of gene regulating protein kinase pathways, a promising target for new anti-inflammatory drug discovery, the indolocarbazole core is not readily amenable to structural diversification of the sort desired for improved formulation properties and minimization of toxicological properties with retention of pharmaceutical effect.